1. Field of the Invention
The present invention relates generally to backlight units. More particularly, the present invention relates to a backlight unit placed on a rear face of a display or between rear faces of two parallel displays to provide back lighting for the display(s).
2. Description of Related Art
Display devices such as liquid crystal displays (LCDs) are commonly used for displays for many electronic devices such as personal digital assistants (PDAs), cellular phones, laptop computers, and televisions, all applications where light weight, low power and a flat panel display are desired. An LCD is essentially a light switching device that does not emit any light on its own. LCDs may be divided into three types: reflective, transflective and transmissive. Reflective LCD use ambient light, and requires no back lighting. However, transmissive and transflective LCDs require back lighting.
In conventional backlit LCDs for televisions, the backlights are cold cathode fluorescent lamps (linear light sources). The linear light sources are placed on a rear face of a display. The area of the display to be lit is a two-dimensional area. The linear light sources are managed by at least one light management feature, which converts linear light sources to light over a two dimensional area, to thereby illuminate The two-dimensional display area.
Referring to FIGS. 30-32, one example of the conventional backlit display devices is described. FIG. 30 is an exploded view of a conventional display device, generally denoted by the reference numeral 10. The display device 10 includes a light control device 12 and a backlight unit 14. FIG. 31 is an exploded view of the backlight unit 14 and FIG. 32 is a cross section taken through the line 32-32 in FIG. 30. The light control device 12 is a liquid crystal display (LCD) having an LCD panel 16 connected to substrates 18 and 20 by means of transmission control protocols (TCPs) 22.
As shown in FIGS. 31 and 32, the backlight unit 14 includes an optical panel 24 that includes at least one light management feature. The at least one light management feature includes a first light management feature within the panel 24 (see FIG. 31) and a second light management feature 26. The first light management feature may include a light diffusing feature. In the illustrated example, the panel 24 is manufactured with the light diffusing feature and thus ma be called a light diffusing panel. The second light management feature 26 may include one or more features such as a brightness enhancement film and/or a light diffusing film. The backlight unit 14 has a light emitting structure 28. The light emitting structure 28 includes a parallel arrangement of a plurality of linear lamps 30 and a power control circuit that includes an inverter substrate 32, a return substrate 34 and a return cable 36.
The backlight unit 14 also includes a chassis 38, a light inflecting cover 40 and a support structure 42 carrying the light emitting structure 28. The support structure 42 includes two spaced cross boards 44 and 46 for holding one and the opposite ends of each of the liner lamps 30. As best seen in FIG. 32, the light inflecting cover 40 has a protrusion 48 (a spacer) that is in contact with the light diffusing panel 24 to keep structural rigidity of the backlight unit 14. The light inflecting cover 40 is pressed into engagement with the chassis 38, to thereby hold the light diffusing panel 24 with the second light management feature 26 in cooperation with the two spaced cross boards 44 and 46 to cover a rectangular opening 50 of the chassis 38. This rigid structure provides a space containing the light emitting structure 28.
Referring back to FIG. 30, the chassis 38 is formed with four mount posts 52. Using these mount posts 52, the chassis 38 supports the LCD panel 16 of the light control device 12 in an appropriate position to cover the rectangular opening 50. In cooperation with a front case 54, the chassis 38 holds the LCD panel 16. The chassis 38 is required to be structurally strong enough to keep the two-dimensional display area on the LCD panel 16 in a desired flat state over its operating life.
Each linear lamp 30 has its life period shorter than the LCD panel 16. Replacing lamps is preferred in order to provide good illumination of the display area over the operating life of the LCD panel 16. The conventional approach for lamp replacement requires disassembling to remove the backlight unit 14 from the front case 54 and the light control device 12. A new backlight unit is reassembled with the front case 54 and the light control device 12. The conventional approach for lamp replacement is disadvantageous because the steps of disassembling and reassembling are time-consuming. The conventional approach for lamp replacement is also disadvantageous because the other components of the removed backlight unit in addition to lamp or lamps to be replaced are abandoned, causing a pick up of maintenance fee. The conventional approach for lamp replacement is further disadvantageous because the LCD panel 16 is left exposed to dust and/or foreign particles within the ambient atmosphere and vulnerable to stains when the backlight unit is removed. The stains on the LCD panel 16 cause local loss in illuminating the display area, to thereby degrade display quality.
Laid-open publication of Japanese UM application H7-16925 discloses a display device wherein a backlight unit is inserted into or removed from a housing of a light control device through an aperture. The backlight unit includes a light shield to cover the aperture. This approach for lamp replacement is disadvantageous because all of the other components of the removed backlight unit in addition to lamp or lamps to be replaced may be abandoned. The conventional approach is also disadvantageous because the light control device is left exposed to the ambient atmosphere through the aperture when the backlight unit is removed.
Referring to FIGS. 33-35, another example of the conventional backlit display devices is described. FIG. 33 is an exploded view of a conventional display device, generally denoted by the reference numeral 60. The display device 60 includes a first light control device 62, a second light control device 64, and a backlight unit 66. FIG. 34 is an exploded view of the backlight unit 66 and FIG. 35 is a cross section taken through the line 35-35 in FIG. 33. The first light control device 62 is a liquid crystal display (LCD) having an LCD panel 68 connected to substrates 70 and 72 by means of transmission control protocols (TCPs) 74. The second light control device 64 is a liquid crystal display (LCD) having an LCD panel 76 connected to substrates 78 and 80 by means of transmission control protocols (TCPs), not shown.
As shown in FIGS. 34 and 35, the backlight unit 66 has a light emitting structure 84. The light emitting structure 84 includes a parallel arrangement of a plurality of linear lamps 86, light inflecting plates 87 (see FIG. 34), a power control circuit that includes an inverter substrate 88, a return substrate 90 and a return cable 92. On one side of the light emitting structure 84, the backlight unit 66 includes a panel 94 that includes at least one light management feature. The at least one light management feature, on the one side of the light emitting structure 84, includes a first light management feature within the panel 94 (see FIG. 34) and a second light management feature 96. On the opposite side of the light emitting structure 84, the backlight unit 66 includes a panel 98 that includes at least one light management feature, too. The at least one light management feature, on the opposite side of the light emitting structure 84, includes a third light management feature within the panel 98 (see FIG. 34) and a fourth light management feature 100. The first and third light management feature may include a light diffusing feature. In the illustrated example, the panel 94 and 98 are manufactured with the light diffusing feature and thus may be called a light diffusing panel. The second and fourth light management feature 96 and 100 may include one or more features such as a brightness enhancement film and/or a light diffusing film.
The backlight unit 66 also includes a first chassis half 102, a second chassis half 104, and a support structure 106 carrying the light emitting structure 84. The support structure 106 includes a first set of spaced cross boards 108 and 110 and a second set of spaced cross boards 112 and 114 for holding one and the opposite ends of each of the linear lamps 86 via rubbers 116 as best seen in FIG. 34.
Referring back to FIG. 33, the first chassis half 102 is formed with four mount posts 118, and the second chassis half 104 four mount posts, not shown. Using the mount posts 118, the first chassis half 102 supports the LCD panel 68 of the first light control device 62 in an appropriate position to cover a rectangular opening 120. Similarly, using the mount posts, not shown, the second chassis half 104 supports the LCD panel 76 of the second light control device 64 in an appropriate position to cover a rectangular opening 122 (see FIG. 35). The first and second chassis halves are pressed into locking engagement with each other to form a whole chassis. In cooperation with the first and second front case 124 and 126, the first and second chassis halves 102 and 104 hold the LCD panels 68 and 76, respectively. The first and second chassis halves 102 and 103 are required to be structurally strong enough to keep the two-dimensional display areas on the LCD panels 68 and 76 in a desired flat state over their operating life.
In the display device 60, as the backlight unit 66 is more complicated and bulky than the backlight unit 14, the disadvantages of the conventional approach for lamp replacement will become more apparent.
It would be desirable to produce improved backlight units and display devices with such improved backlight units, which allow replacement of light source or sources with less time, cost, and difficulty, and with little probability of staining a display panel to be lit during replacement of light source or sources.